RNA polymerase II (Pol II) elongation control plays a major role in regulating transcription throughout development and differentiation of multi-cellular organisms. The process is characterized by the default action of negative elongation factors, including NELF and DSIF that halt transcription of initiated polymerases near promoters. These promoter proximal paused polymerases are either released from the template by TTF2 or other termination factors or are allowed to enter productive elongation through the selective action of the positive elongation factor, P-TEFb. The cyclin dependent kinase activity of P-TEFb is regulated by reversible association with the 7SK snRNP mediated by HEXIM proteins. The main goal of this proposal is to further define the mechanisms utilized to control Pol II elongation. The approach will employ biochemical and molecular methods in human cells. The first aim will explore the role of Gdown1 in the regulation of Pol II elongation. The plan includes in vitro biochemical approaches to purify the Gdown1 negative accessory factor, GNAF, and to purify and characterize a Gdown1 kinase that controls TTF2 dependent termination. In the second aim studies in vitro and in cells will determine mechanistic details of the control of P-TEFb by the 7SK snRNP. The plan describes methods to study the recruitment of P-TEFb to genes to be activated in which the role of the 7SK snRNP will be determined. The regulated release of P- TEFb from the 7SK snRNP by Brd4 and other factors as well as the critical step of re-sequestration of P- TEFb into the 7SK snRNP will be studied. The goal of the final aim is to identify productive elongation factors and determine how they are involved in the transition into and maintenance of productive elongation. The principle investigator is a professor at the University of Iowa and this project wil be carried out in the excellent environment offered by his lab and the facilities in the University of Iowa, Carver College of Medicine. The studies proposed here should significantly increase our understanding of mechanisms controlling gene expression and this will be useful in explaining the disregulation of transcription that occurs in cancer and the hijacking of elongation control machinery by the AIDs virus.